The invention relates to nematic liquid-crystal compositions based on bisalkenyl compounds and terminally fluorinated compounds. These compositions are particulary suitable for plasma-addressed display devices.
Plasma-addressed displays (PADs) are of great utility for high-information displays, which are of commercial interest. Such PADs are used in TV applications and in high-information displays for computer screens, automobiles and aircraft.
PADs have electrical switching elements and a plasma cell with a plurality of addressing channels which is connected to the display cell.
Such PADs are disclosed, for example, in WO 96/00925, EP 0 628 944, EP 0 545 569, U.S. Pat. No. 4,896,149 and U.S. Pat. No. 5,077,553.
In a PAD, the switching elements are addressed via a multiplexing scheme. This charges the electrodes of a pixel in the limited time during which they are active. They subsequently become and remain inactive until they are addressed again in the next cycle. Consequently, the voltage change at a plasma-addressed pixel is an unwanted, but very crucial characteristic of such a display. Discharge of the electrodes of the pixel is determined by two factors, the capacity of the pixel and the specific resistance of the liquid-crystal material, i.e., the liquid crystal, between the electrodes.
Conventional liquid-crystalline materials for active matrix displays (AMDs) are unsuitable for PADs since they have excessively high values for the dielectric anisotropy.
There therefore continues to be a great demand for liquid-crystal compositions having high specific resistance and having other material properties which are suitable for use in PADs, such as, for example, a broad nematic mesophase range with an extremely low smectic-nematic transition temperature and the absence of crystallization at low temperature.
A further requirement in such compositions is for high steepness of the characteristic lines (small difference between V.sub.90 and V.sub.10)